Since a few years there has been increasing interest within the detergents industry to produce more concentrated fabric washing detergent powders having a relatively high bulk density, for example of about 500 g/l and above.
There are two basic types of processes by which base powders for detergent powders can be prepared. The first type involves spray-drying an aqueous detergent slurry in a spray-drying tower, and in the second type of process, the various components are dry-mixed and optionally agglomerated with liquids, e.g. nonionics.
The dominant factor governing the bulk density of a detergent base powder is the bulk density of the starting materials in the case of a dry-mixing process, and, in the case of a spray-drying process, the chemical composition of the slurry, in particular the ratio between the organic and inorganic materials. For example, the bulk density of a dry-mixed powder may be increased by increasing its content of relatively dense sodium sulphate. However, the latter does not contribute to the detergency of the powder, so that its overall properties as a fabric washing powder will generally be adversely affected.
Therefore, a substantial increase in bulk density can only be achieved by additional processing steps and several processes have been described in the art. Particular attention has thereby been paid to the densification of spray-dried powders by post-tower treatment.
The Japanese patent application 61 069897 (Kao) discloses a process in which a spray-dried detergent powder containing a high level of anionic surfactant and a low level of builder (zeolite) is subjected successively to pulverizing and granulating treatments in a high-speed mixer/granulator, the granulation being carried out in the presence of an "agent for improving surface properties" and optionally a binder. It would appear that in the high-speed mixer/granulator, the spray-dried powder is initially broken down to a fine state of division; the surface-improving agent and optional binder are then added and the pulverized material granulated to form a final product of high bulk density. The surface-improving agent, which is a finely divided particulate solid such as fine sodium aluminosilicate, is apparently required in order to prevent the composition from being formed into large balls or cakes.
The British patent application 1,517,713 (Unilever) discloses a batch process in which spray-dried or granulated detergent powders containing sodium tripolyphosphate and sodium sulphate are densified and spheronized in a "marumerizer" (Trade Mark). This apparatus comprises a substantially horizontal, roughened, rotatable table positioned within, and at the base of, a substantially vertical, smooth-walled cylinder.
The British patent application 1,453,697 (Unilever) discloses the use of a "marumarizer" for granulating together detergent powder components in the presence of a liquid binder to form a granular detergent composition.
The European patent application 220,024 (Procter & Gamble) discloses a process in which a spray-dried detergent powder containing a high level (30-85% by weight) of anionic surfactant is mixed with an inorganic builder (sodium tripolyphosphate, or sodium alumino-silicate and sodium carbonate) and compacted under high pressure using a roll compactor ("chilsonator"); the compacted material, after removal of oversize material and fines, is then granulated using conventional apparatus, for example a fluidized bed, tumble mixer, or rotating drum or pan.
The European patent application 265,203 (Unilever) discloses a process in which a rather different approach is taken. According to this process, first a liquid surfactant composition is prepared which is mobile at a temperature within the range of 20.degree. to 80.degree. C. and which comprises a sodium or potassium salt of an alkylbenzene sulphonate or alkyl sulphate in an amount not exceeding 80% by weight; an ethoxylated nonionic surfactant in an amount not exceeding 80% by weight; and water in an amount not exceeding 10% by weight. This liquid surfactant composition is then sprayed onto a solid particulate absorbent material, for instance a porous spray-dried base powder having a low bulk density and containing no or little actives, to form a detergent base powder having an increased bulk density.
The above process gives good results in the preparation of phosphate containing detergent compositions. However, when the process was used to prepare a phosphate-free washing powder from a zeolite containing absorbent material, it was found that these denser powders have a tendency to dispense less well in European type automatic washing machines; a relatively high proportion of the powder dosed into the machine is left behind in the dispenser drawer, leading to powder wastage, clogging and poor washing results. This problem is especially marked at low wash temperatures and the use of a shuttle may be required in order to obtain satisfactory washing results.
It is therefore an object of the present invention to provide an improved process of the above-mentioned kind for obtaining phosphate-free detergent compositions or components thereof, having a bulk density of at least 500 g/l, or indeed compositions which also comprise phosphate.
We have now found that an improvement with regard to the dispensing properties may be obtained in the above process if 0.5-80% by weight of a C.sub.8 -C.sub.22 fatty acid is incorporated in the liquid surfactant composition which is sprayed onto the solid material.